<script>
    // const a = [{k1:1, k2:2}];
    // const b = JSON.parse(JSON.stringify(a))
    // b[0].k1 = 2;
    // console.log( a[0].k1 ) 
    const arr = [0,1,2,[3,4,[5]],3,[1]]
   console.log(arr.reduce((result,val)=>result.concat(val),[])); 
   const Arr = [].concat(...arr);
   const ARR = [].concat(...Arr)
   console.log(ARR);
</script>